It is known that air column resonance occurring in a tire air chamber formed between a tire and the rim of a wheel causes road noise of an automobile. Air column resonance refers to a resonance phenomenon that a random vibration input transmitted to a tire tread from a road surface during driving vibrates air in a tire air chamber wherein the resonance phenomenon occurs near the vibration frequency of air column resonance in the tire air chamber. This resonance phenomenon generates air column resonance sound in the tire air chamber. When air column resonance sound is generated in the tire air chamber, this air column resonance sound vibrates the wheel, and the vibration is transmitted to the vehicle body through a suspension and is felt as a road noise in the vehicle compartment.
As a wheel that reduces such a road noise, various ones provided with Helmholtz resonators, each having a sub air chamber which communicates with a tire air chamber via a communication hole, are presented (for example, refer to Patent Literatures 1 to 3).
Conventionally, such a wheel is often provided with more than three Helmholtz resonators at equal intervals along the circumferential direction of the wheel so that vibration applied by air column resonance sound can be sufficiently reduced. On the other hand, in order to reduce the manufacturing cost of a wheel, simplify the manufacturing process of the wheel, and reduce the weight of the wheel, reduction in the quantity of Helmholtz resonators is desired.